Mike Siless
New User
I have a '67 424 with a newer Zenith carb. Just had head and valves done, timing, and electronic ignition added. Initial carb setting at 3/4 turn on the idle screw and 3 turns on the high speed screw. After warm up got a good idle by going out to 1 turn. At full throttle it was breaking up, turning the high speed screw in made it worse, backing it out improved it but not completely. I stopped at 2 1/4 turns, going farther out made no difference. Still at full throttle I tried turning the IDLE screw in to 1/2 turn and it cleared right up! It sounds perfect at full, but is now a little rich at idle. My question is, why does the idle screw have any affect at full throttle? 1/2 turn to 5/8 on the idle screw is good, but as soon as you turn it out to 3/4 it starts breaking up at full throttle.
